Can anyone identify this tree for me, please? It's been grown from a seed I picked up in Kew Gardens in London many years ago. It seems to be very happy in my garden and is now about 3 metres tall. The leaves, when crushed, have a very sweet, slightly medicinal smell. Any help would be appreciated.

UPDATE, thanks for your replies, here's a couple of pictures which may give you a bit more information. Again, many thanks for your help

Hi, Derek
It can be Juglans regia (Walnut tree). Almost sure...:)
This tree grows very tall and big and it's not for small gardens. It gives a deep shadow and very hard to remove because of its strong root system.

It might also be a Black Walnut (Juglans nigra). It's supposed to have fragrant leaves too. I don't remember Arizona Black Walnuts having fragrant leaves, but that's a different species (Juglans major). Also, it's been a while since I've had one in smelling range! : D

Hi all, many thanks for your swift and knowleadgable replies. Having looked through them and suddenly remembering what the seed looked like I have come to the conclusion that it's a Fragrant Ash.
Again, many thanks for your help